The present invention relates to a method for controlling absorbent at a decarboxylation facility and a system therefor.
In recent years, at thermal electric power plants and boiler plants, a large amount of coal, heavy oil, or superheavy oil has been used as a fuel, so that the control of the quantity and concentration of discharged sulfur oxides mainly consisting of sulfur dioxide, nitrogen oxides, carbon dioxide, and the like has posed a problem from the viewpoint of prevention of air pollution and cleanness of global environment. Also, for carbon dioxide, together with flon gas and methane gas, the control of its discharge has been studied form the viewpoint of global warming. Therefore, methods such as a PSA (Pressure Swing Adsorption) method, a membrane separation concentration method, and a reaction absorption method using a basic compound have been studied. U.S. Pat. No. 5,318,758 has disclosed a method for effecting decarboxylation with an amine compound (hereinafter referred simply to as amine) being used as an absorbent. In this method, if the balance between the quantity of water in combustion flue gas flowing into a decarboxylation facility and the quantity of water in absorbent flowing out of the decarboxylation facility together with gas is lost, or amine in absorbent flows out of the decarboxylation facility, the concentration of amine in absorbent is liable to vary. The variations in amine concentration cause variations in the absorption rate of carbon dioxide and steam consumption in a regeneration tower.
Conventionally, in order to make the amine concentration constant, water containing amine is extracted from an overhead drum of the regeneration tower, or the operator regulates the gas temperature at the inlet or outlet of an absorption tower manually to control the water balance. Therefore, the burden on the operator is heavy, and the cost of waste water treatment facility is excessive.
An object of the present invention is to provide a method for controlling absorbent at a decarboxylation facility, in which water balance is controlled automatically and the concentration of amine is automatically kept proper, and a system for carrying out this method.
To achieve the above object, the present invention provides a method for controlling an absorbent at a decarboxylation facility provided with an absorption tower having an amine recovery section and a regeneration tower, wherein a temperature controller for circulating water to the washing section of the absorption tower is controlled by a controller of the liquid level of the bottom of the absorption tower to control the temperature of the circulating water, thereby the concentration of amine in the absorbent is regulated.
In the present invention, the controller of the liquid level of the bottom of the absorption tower is generally a liquid level controller, which receives liquid level information sent from a liquid level detector and sends a control signal to the temperature controller.
The temperature controller for circulating water to the washing section of the absorption tower is generally a temperature controller, which receives a control signal sent from the controller of the liquid level of the bottom of the absorption tower and changes a temperature set value, and regulates the flow rate by controlling a control valve while detecting temperature information sent from a temperature detector.
Also, the present invention provides, in another embodiment, a method for controlling absorbent at a decarboxylation facility provided with an absorption tower having an amine recovery section and a regeneration tower, wherein a temperature controller for circulating water to a cooling tower for the absorption tower is controlled by a controller of the liquid level of the bottom of the absorption tower to control the temperature of the circulating water, whereby the concentration of amine in the absorbent is regulated.
The temperature controller for circulating water to a cooling tower for the absorption tower is generally a temperature controller, which receives a control signal sent from the controller of the liquid level of the bottom of the absorption tower and changes a temperature set value, and regulates the flow rate by controlling a control valve while detecting temperature information sent from a temperature detector.
In the present invention, the control method using the controller of the liquid level of the bottom of the absorption tower preferably involves sample PI control. In this case, even if a delay exists in the operation result, control can be accomplished properly.
Further, the present invention provides, as another aspect, a system for controlling absorbent at a decarboxylation facility provided with an absorption tower having an amine recovery section and a regeneration tower, wherein the system comprises a controller of the liquid level of the bottom of the absorption tower and temperature controller for circulating water to the washing section of the absorption tower controlled by the controller of the liquid level of the bottom of the absorption tower.
Such a control system comprises, in another embodiment, a controller of the liquid level of the bottom of the absorption tower and a temperature controller for circulating water to a cooling tower for the absorption tower controlled by the controller of the liquid level of the bottom of the absorption tower. Such a control system comprises, in still another embodiment, a controller of the liquid level of the bottom of the absorption tower, a temperature controller for circulating water to the washing section of the absorption tower controlled by the controller of the liquid level of the bottom of the absorption tower, and a temperature controller for circulating water to a cooling tower for the absorption tower controlled by the controller of the liquid level of the bottom of the absorption tower, so that the temperature controller system for the circulating water to the washing section and the temperature controller system for the circulating water to the cooling tower are operated by being switched alternately.
In the present invention, water balance is controlled automatically and the concentration of amine is automatically kept proper. In the embodiment, in which the temperature of the circulating water is controlled, of water content in circulating amine solution, water content lost by accompanying outlet gas is controlled, by which the concentration of amine is regulated. Also, in the embodiment in which the temperature of the circulating water to the cooling tower is controlled, the water content added by accompanying inlet gas, which is one factor that determines the water content in circulating amine solution, is controlled, by which the concentration of amine is regulated.